Stackable seat



FIG. 1 is a perspective view as seen from the front and upper right of a stackable seat showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a left side elevational view thereof, the right side is symmetrical;

FIG. 4 is a top plan view thereof; and,

FIG. 5 is a rear elevational view thereof.

The broken line illustration in the drawing disclosure of the seat member is for illustrative purposes of environment and forms no part of the claimed design. 

The ornamental design for a stackable seat, as shown and described. 